The invention relates to a threshing mechanism comprising first and second threshing drums disposed one behind the other, a first concave enclosing the first threshing drum and the second threshing drum in sections in the circumferential direction and, a second concave enclosing the second threshing drum in sections in the circumferential direction. The concaves are displaceable in the radial direction of the threshing drums and at least one crop-processing device is disposed at the first concave.
A threshing mechanism of the initially described type is known from EP 0 745 317 A1. EP 0 745 317 A1 describes a threshing mechanism that operates according to the principle of tangential flow and comprises at least two threshing drums disposed one behind the other and are driven in the same direction, with concaves assigned thereto. The first concave, which encloses the first threshing drum, is angled in the region thereof facing the second threshing drum and, there, comprises a crop-processing device designed as a friction or threshing element and is displaceably supported in the frame of the first concave. The concaves can be adjusted by a lever arrangement in the radial direction of the threshing drums, thereby changing the concave gap in order to permit adaptation to different types of crops to be processed. While the first concave is displaceable parallel to itself, the second concave is rotatably supported at the end thereof facing away from the first concave. As a result, when the distance of the two concaves from the first and the second threshing drum is jointly adjusted, the respective inlet gap at the first and the second threshing drum is changed in the same direction.
By contrast, the gap profile between the second threshing drum and the first concave, which wraps around this second threshing drum in sections, and the second concave is characterized by an increasingly convex profile as the concave separation is adjusted with increasing separation from the thrashing drums. This means that the gap profile from the inlet gap between the first concave and the second threshing drum to the outlet gap between the second concave and the second threshing drum follows a non-uniform, bulged course. This arrangement has an unfavorable effect on the crop flow and the quality of the threshing process.